1. Field of the Invention
The present invention relates to a developing device in which an electrostatic latent images formed on an image carrier is converted into a visible image in an image forming apparatus such as electrophotographic apparatus or electrostatic recording apparatus.
2. Description of the Related Art
A developing device in which a non-magnetic toner is used is known. This type of developing device includes a rotatable developing roller for supplying the non-magnetic toner to an image carrier such as a photosensitive drum. The developing roller receives the non-magnetic toner from a toner hopper in which the non-magnetic toner is contained. A toner supply roller, which is located in the toner hopper, rotates in the same direction as the developing roller to transport the non-magnetic toner to the developing roller. Then a toner thin layer is formed on the surface of the developing roller by a thin layer forming member which is in linear contact with the developing roller at a uniform pressure. The thin toner layer passes close to, or into contact with, the image carrier holding an electrostatic latent image to form a toner image on the image carrier.
However, there was a problem in the above-mentioned conventional developing device in that the capacity for transporting toner to the developing roller was insufficient. For instance, when printing a whole-surface solid image on paper, the image density at the trailing edge of the paper was less than that of the image density at the leading edge.
Also, poor toner layer formation occurred when executing continuous printing operations using the above conventional developing device. This resulted in reduction of image density.
Japanese Laid Open Patent No. 62-211674 discloses a developing device including a corona charger so called a corotron is located in the toner hopper for electrofying a non-magnetic one-component toner. The corotron comprises a conductive case and a corona wire. Since the case has an opening portion, the toner will intrude into the case. As a result, the case is filled by the toner. Therefore, corona charging operation will not perform sufficiently.